Ex 15.1

Chapter 15 Class 10 Probability
Serial order wise   This video is only available for Teachoo black users  This video is only available for Teachoo black users  This video is only available for Teachoo black users

Solve all your doubts with Teachoo Black (new monthly pack available now!)

### Transcript

Ex15.1, 18 A box contains 90 discs which are numbered from 1 to 90. If one disc is drawn at random from the box, find the probability that it bears a two-digit number Total number of discs = 90 Number of two digit numbers in the discs = 10,11,12,13,14……90 Counting number of two digit numbers 10, 11, 12, 13……90 Since difference between consecutive numbers is same, These numbers form an A.P. First number = a = 10 Common difference = d = 11 – 10 = 1 Last number = an = 90 an = a + (n-1)d 90 = 10 + (n-1) 1 90 = 10 + n - 1 90 = 9 + n n = 90 – 9 n = 81 ∴ Total number of two-digit numbers between 1 and 90 = 81 So, Total number of discs with two digit numbers = 81 P (getting a two-digit number) = (𝑇𝑜𝑡𝑎𝑙 𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑑𝑖𝑠𝑐𝑠 𝑤𝑖𝑡ℎ 𝑡𝑤𝑜 𝑑𝑖𝑔𝑖𝑡 𝑛𝑢𝑚𝑏𝑒𝑟)/(𝑇𝑜𝑡𝑎𝑙 𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑑𝑖𝑠𝑐𝑠) = 81/90 = 9/10 Ex15.1, 18 A box contains 90 discs which are numbered from 1 to 90. If one disc is drawn at random from the box, find the probability that it bears (ii) a perfect square number Total number of discs = 90 Perfect square number is a number like 1 (= 12) , 4 (= 22) , 9 (= 32) , 16 (= 42), 25(= 52) , 36 (= 62) , 49 (= 72) , 64 (= 82), 81 (= 92) Total number of discs with perfect square number = 9 P (getting a perfect square number) = (𝑇𝑜𝑡𝑎𝑙 𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑑𝑖𝑠𝑐𝑠 𝑤𝑖𝑡ℎ 𝑝𝑒𝑟𝑓𝑒𝑐𝑡 𝑠𝑞𝑢𝑎𝑟𝑒 𝑛𝑢𝑚𝑏𝑒𝑟)/(𝑇𝑜𝑡𝑎𝑙 𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑑𝑖𝑠𝑐𝑠) = 9/90 = 1/10 Ex15.1, 18 A box contains 90 discs which are numbered from 1 to 90. If one disc is drawn at random from the box, find the probability that it bears (iii) Number divisible by 5 Total number of discs = 90 Numbers divisible by 5 are 5 , 10, 15, 20 , 25 , 30 , 35 ,40 , 45 , 50 , 55 , 60 , 65 , 70 , 75 , 80 , 85 , 90 Total number of numbers on the disc divisible by 5= 18 P (getting a number divisible by 5) = (𝑇𝑜𝑡𝑎𝑙 𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑑𝑖𝑠𝑐𝑠 𝑤𝑖𝑡ℎ 𝑛𝑢𝑚𝑏𝑒𝑟𝑠 𝑑𝑖𝑣𝑖𝑠𝑖𝑏𝑙𝑒 𝑏𝑦 5)/(𝑇𝑜𝑡𝑎𝑙 𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑑𝑖𝑠𝑐𝑠) = 18/90 = 1/5 